Problem with Machined Extractors

[Synchronizor]

I'm in research mode for a T&T video on 870 extractors, and I came across this thread from 2010 talking about how some recent machined extractors were manufactured without a chamfer on the top edge.

MIM extractors all feature this chamfer because they're molded in one shot like injection-molded plastic parts; but non-MIM extractors are shaped in discrete, separate steps, and it seems the chamfering step was being skipped.

Extractor Bevel 1.JPG (39.55 KiB) Viewed 7256 times

Extractor Bevel 2.JPG (75.83 KiB) Viewed 7256 times

This chamfer makes the extractor conform more closely to the exterior profile of the breech bolt. Without the chamfer, the sharp corner will stick out from the bolt and scrape the inside of the receiver when the action is opened. Over time, that corner will cause a deeper-than-normal gouge in the receiver.

Extractor Bevel 3.JPG (61.02 KiB) Viewed 7256 times

This shouldn't cause any function problems or structural weaknesses, but it is unsightly, and may increase the chances of corrosion.

Now, I haven't seen any reason to replace the MIM extractor in my 870, but based on images of machined extractors that I've come across, it looks like they're still being made without the chamfer.


So, for those of you who have recently purchased an 870 with a machined extractor, or have ordered one separately to replace a MIM extractor, was your extractor chamfered or not? And if it wasn't, has that corner caused any extra wear or other problems?

[EdwardE]

Synchronizor,
I have the MIM in the 81998. I noticed two differences in mine vs. the pics you posted. First, the chamfer on mine is not nearly as large as the one in the pics. At most, maybe a 64th of an inch at its widest point. Its almost a stretch to call it chamfered. The other difference is that there is a machined slot in the reciever in line with the extractor. This slot is wide enough to accomodate the width of the extractor, and then some. It looks to be impossible to carve a groove into the reciever if switched to a non-MIM. My reciever is dated 1998. I wonder if this extractor slot appeared alongside the arrival of the milled extractor or was s solution to the carving problem?

[Synchronizor]

I have the MIM in the 81998. I noticed two differences in mine vs. the pics you posted. First, the chamfer on mine is not nearly as large as the one in the pics. At most, maybe a 64th of an inch at its widest point. Its almost a stretch to call it chamfered.

The chamfer isn't that big, it's just enough to take the edge off.

The other difference is that there is a machined slot in the reciever in line with the extractor. This slot is wide enough to accomodate the width of the extractor, and then some. It looks to be impossible to carve a groove into the reciever if switched to a non-MIM. My reciever is dated 1998. I wonder if this extractor slot appeared alongside the arrival of the milled extractor or was s solution to the carving problem?

Are you sure your gun is from 1998? I don't think the 81198 Express Tactical (assuming that's what you have) has been around that long.

The machined extractors are not new parts, they were used in the original 1940s 870 design (and the semi-auto shotguns it was based on). The MIM extractors came later, once Remington had developed and refined the metal injection technology enough to make it cost-effective, and ensure that the parts would have acceptable material properties and dimensional tolerances. Both machined and MIM extractors should have a chamfered top edge, but it seems some of the newer machined ones are being manufactured without it.

Remington doesn't machine an extractor groove into their 870 receivers, that's a wear notch caused by the extractor. If the notch on your gun looks like it clears the extractor with room to spare, you probably don't have a shell rim underneath it. Next time you're in a gun store, look at one of their new 870s, and you'll see that there's no notch there yet. Just like the dents that develop inside the receiver where the locking block taps against the roof, this is a wear mark that the gun will develop as it's broken in. This notch is normal even with a properly-shaped extractor (and it demonstrates why the designers went with a solid steel receiver), but if the extractor's sharp corner isn't taken down, it will cut a larger, deeper gouge more quickly.

extractor notch 1.JPG (49.35 KiB) Viewed 7211 times

extractor notch 2.JPG (90.93 KiB) Viewed 7211 times

[EdwardE]

Thanks for the clarification on the extractor.
Have you ever looked at something, walked away and then came back to it? And now you realize just what you thought you were looking at wasn't that at all. That's me. Right now. My bad. I need a vacation.

As for the serial number, I'm not ruling out me incorrectly reading the stamp. Now I know why the wife bought me those reading glasses!

so, a MIM will carve a notch in the reciever (though not as large or qiuckly as an un-modified non-MIM) anyway?

[Synchronizor]

As for the serial number, I'm not ruling out me incorrectly reading the stamp. Now I know why the wife bought me those reading glasses!

You may have just entered the wrong thing. Currently, that page is pretty poorly-worded, referring to a "serial number". The alpha-numerical serial number on the gun's receiver is not the same thing as the 2- or 3-letter date stamp on the side of the barrel, so if you entered the first two letters of your gun's actual serial number, the lookup function on that page is almost always going to spit out the wrong date. In addition to the 81198 model being a fairly recent offering, what made me strongly suspect that this is what you did is that you mentioned in your introduction thread that you recently purchased your 870, and the "RS" serial number prefix of a current- or recent-production 870 will point to a November 1998 manufacturing date if those two letters are incorrectly analyzed as a date stamp.

so, a MIM will carve a notch in the reciever (though not as large or qiuckly as an un-modified non-MIM) anyway?

Any extractor will wear a notch into the rear edge of the ejection port, MIM or machined. Even if the extractor doesn't touch the receiver otherwise, when a shell is being ejected, it will tend to push the extractor out enough to make contact. Again, this is why the 870 has a steel receiver; it doesn't wear out, it wears in. Once enough shells have been cycled through the gun, the extractor (whether it's chamfered or not) will have cleared enough space to function without ever catching on or rubbing against the receiver, and the gun will function more smoothly.

When you hear people bad-mouth the 870 because it doesn't have the same lightweight, rust-proof aluminum or polymer construction as its competitors, just smile and nod, and know that someday your grandkids could be teaching their kids how to work your 870, while those other "space-age" guns have long since been recycled into beer cans or cell phones.

[Ace of Spades]

My Rem 870 Tactical Express is a 2012/2013 model. I haven't gone into the date codes but I expect it is this age because I bought it six months ago. I bought a non-mim extractor from Brownells about six weeks ago and it has exactly the same chamfer as the non-mim. I do have wear on the extratcor port exactly as you describe but I can't say for sure which extractor caused this. However it is very minimal. My guess is the non-mim is much harder steel than the non-mim even with the chamfer. So harder steel rubbing against softer steel is going to cause this even with a chamfer.

[Synchronizor]

I bought a non-mim extractor from Brownells about six weeks ago and it has exactly the same chamfer as the non-mim.

That's good to hear, and I've heard others saying the same. Hopefully the issue has been fixed, and extractors are being machined properly again.

I do have wear on the extratcor port exactly as you describe but I can't say for sure which extractor caused this. However it is very minimal. My guess is the non-mim is much harder steel than the non-mim even with the chamfer. So harder steel rubbing against softer steel is going to cause this even with a chamfer.

Not sure what you meant to say there. If you're thinking the machined extractors are harder than the MIM extractors, that's probably not true. Metal injection molding is a big step above traditional powder metallurgy technology. Done properly, injection molded metal has 95 - 99% the density of the same wrought material, with virtually identical mechanical properties and very tight tolerances. Through heat-treating and composition adjustment, and with experienced part & mold design, there's no reason Remington can't produce MIM extractors that are as hard as they need to be, especially considering that Remington has their own Powdered Metal Products Division for developing MIM technology and manufacturing parts.

In any case, both MIM and machined extractors are harder than the steel of the receiver, and will carve a notch in the same place as the gun breaks in. This is my 870, and it's only ever had the factory MIM extractor.

The chamfer won't prevent this notch from forming, but it will make it less severe.

[Ace of Spades]

Not sure what you meant to say there. If you're thinking the machined extractors are harder than the MIM extractors, that's probably not true. Metal injection molding is a big step above traditional powder metallurgy technology. Done properly, injection molded metal has 95 - 99% the density of the same wrought material, with virtually identical mechanical properties and very tight tolerances. Through heat-treating and composition adjustment, and with experienced part & mold design, there's no reason Remington can't produce MIM extractors that are as hard as they need to be, especially considering that Remington has their own Powdered Metal Products Division for developing MIM technology and manufacturing parts.

In any case, both MIM and machined extractors are harder than the steel of the receiver, and will carve a notch in the same place as the gun breaks in. This is my 870, and it's only ever had the factory MIM extractor.

The chamfer won't prevent this notch from forming, but it will make it less severe.[/quote]

What I meant to say is that the non-mim extractor looks as if it is made from machine steel, the type used for cutting tools. It's edges are sharper than the mim. I don't know if it is forged but it looks that way. However you are perfectly correct both mim and non-mim are certainly harder than the receiver. Any ideas why the mim has that raised notch on the top?

[Synchronizor]

What I meant to say is that the non-mim extractor looks as if it is made from machine steel, the type used for cutting tools. It's edges are sharper than the mim.

Well, a molded edge can only be made so sharp without causing issues during molding. Conversely, a machined edge is sharp to start with, and extra steps are required to make it otherwise. So the sharpness of the edge there really doesn't say much about the actual properties of the material. And obviously, there's no need for a razor edge there; if anything, an overly sharp and delicate edge will just promote breakage.

Any ideas why the mim has that raised notch on the top?

I'm pretty sure that's a gate mark, indicating the location where the metal particle/binder feedstock paste was injected into the mold. Gate marks can be minimized through mold design and precise feedstock control, but they can't be avoided completely, and extra precision always means extra cost in the manufacturing world. Trying to reduce the gate mark could also go too far and cause a negative mark - a concavity or notch instead of a ridge - which would weaken the part.

By placing the gate on this outside face, the mark left behind becomes a non-issue. It will have no effect on function there, so there's no need to spend extra money and effort on ultra-precise feedstock control or additional finishing processes. That spot is also a nice centralized location, minimizing the distance the feedstock has to travel to fill the entirety of the mold. This reduces the likelihood of various defects, and improves part quality & consistency. Plus, it's a convenient identifying mark.

You can find a decent overview of good MIM mold & part design practices here, and a simplified diagram of the MIM process here. Remington really knows what they're doing with this.

[Ace of Spades]

Synchronizor thanks for the info. Great to be able to talk about the finer points of the 870 with someone who really knows.